Patent GB-644316-A (GB)
Title: Improvements in telephone switching and signalling systems
IPC: H04Q1/44
Filed: 1947-03-04
Abstract: 644,316. Automatic exchange systems. O'DELL, A. E. (Punch Engineering Pty., Ltd.). March 4, 1947, No. 6171. [Class 40 (iv)] At a tandem exchange at which lines using different signalling systems terminate signalling equipment is permanently associated with each of the different types of lines for the reception and transmission of basic line signals and voice frequency receivers are selectively connectable with each of a plurality of the lines to receive and translate dialling pulses or number codes and auxiliary signals. The invention is described with respect to two types of line; the upper line in the drawings being one in which basic line signals are transmitted by voice fre. quencies above the range used for speech, and the lower line being a carrier channel in which the carrier is normally suppressed but is transmitted to send basic line signals over the channel. Carrier channel. When the operator 1 (Fig. 1) plugs into an outgoing line relay 3 pulls up for the duration of the call. Relays 4 and 5 follow and 6 operates during the operate time of 7 to send a pulse of carrier from oscillator 8 to line. This pulse operates pulse receiver 12 (Fig. 2) whereupon relays 13 and 14 pull up momentarilydisconnecting the normallyoperated relay 15 and bringing up 16 which locks up with 15. The consequent operation of 17 energizes the magnet 18 of a line-finder with banks 22 to 27 over a back contact of its test relay 29. A second similar line-finder is indicated by magnet 19 and is operated in the same way over a back contact of relay 75 (not shown). These finders commence hunting for the calling line the test relay, e.g. 29, coming up over bank 22 on finding, in series with relay 28, whereupon 17 relapses and cuts the drive of the finders. The operation of 29 prevents magnet 18 being operated again during the call, shortcircuits its own high resistance winding to prevent a second finder from stopping in the same position, and connects up the V.F. receiver 30 (Fig. 5) over banks 23 and 24. Relay 32 pulls up over bank 25 and the selector 33 is'seized, while the wipers of banks 26 and 27 are connected to the V.F. line 31. The operator dials, V.F. impulses being injected at 37 (Fig. 1) and passing over the speech path to the receiver 30 and thence via the band-pass filter 38 to the grid of valve 39 whereby relay 40 responds to the impulses dialled and repeats them to relay 32 which controls the selectors of the switch train. After the wanted subscriber's number has been dialled ringing is initiated by the operator depressing a ring key to send a distinctive frequency signal over the line. This signal passes via band-pass filter 41 to valve 42 in the receiver 30 and operates relay 43 thus connecting the ringing generator 44 to the talking leads. On the reply of the called party, relay 45 (Fig. 4) pulls up to reversed battery, holds 32, and brings up 47 (Fig. 3), followed by 48. Relay 49 (Fig. 2) then comes up during the operate-time of 50 to send a pulse from the carrier oscillator 51 over the line to operate relay 55 in the carrier receiver 54 thus bringing up 56 which momentarily disconnects the normally-operated relay 57 and operates 58 which locks up with 57. The consequent operation of 59 reverses the battery over the line to the operator. Speech passes over the established connection in the normal manner, oscillators 8 and 51 supplying the carrier wave. When the operator clears down the release of relay 3 is followed by that of 4 and 5, and relay 6 comes up during the release time of 7 to send a long carrier pulse to line. Relay 15 releases to the long pulse and 16 falls away followed by 32, 17, 28, 29 and 45 and the selectors are released. Relay 45 releases 47, 48 and 50, 49 coming up during their release time to revert a long " clear " pulse of carrier which brings about the release of 57 (Fig. 1). The consequent relapse of 58 restores the circuit to normal. Tandem connection. The originating operator is connected with the V.F. receiver at the tandem point as described above and sends V.F. pulses to select an outgoing line to the far end V.F. receiver. When this selection is completed ground is returned over the private wire to bring up relay 71 (Fig. 5). Relay 32 is thus locked to prevent it responding to further incoming signals and such signals pass through the tandem exchange to the far end V.F. receiver. Recalling operator at tandem or terminating exchange. For this purpose an auxiliary signal of distinctive frequency is sent by the originating operator and is applied via band-pass filter 72 to the grid of valve 73 to operate 74 and signal the operator required. V.F. line. The operator 1<SP>1</SP> (Fig. 1) plugs into an outgoing line whereupon relays 31 and 51 pull up and V.F. current from oscillator 76 (Fig. 2) is sent to line received in receiver 80 and operates relay 16<SP>1</SP>. Relay 17<SP>1</SP> follows and line finders 18 and 19 commence hunting for the line 81. Relay 32<SP>1</SP> is impulsed and the selectors 82 are set, whereafter operation of relay 43 connects up ringing current. On the reply of the called party operation of 45<SP>1</SP> releases the V.F. receiver 30, locks up 32<SP>1</SP>, and brings up 491 to revert V.F. current from oscillator 79. Relay 581 responds, bringing up 591 to reverse the polarity at the originating exchange. Release is under the control of the originating operator.